The present invention relates to improved electronic memory systems and more particularly to an improved electronic memory system incorporated into electronic postage meters for the purpose of maintaining a running account of the functions performed by the postage meter, particularly the accumulated amount of postage dispensed by the postage meter.
For the most part, postal meters on the market today are rental devices The meters are rented by the customer and usually retained and used on the premises of the customer.
Routine servicing of the meter, such as taking readings of the registers and/or setting postage tables is usually done in the field by Postal Service representatives or other authorized service personnel. However; when a postage meter breaks down, the down meter is returned to the owner or manufacturer and a substitute postage meter is provided to the customer. The customer renting the postage meter makes no repairs or adjustments to the meter. The customer does, however, set the postage value to be printed. Bench repairs and/or adjustments, other than routing servicing, are normally made by authorized service personnel or employees of the manufacturer authorized to make such repairs and/or adjustments.
A system of this nature requires a substantial service organization to effect exchange of the down meter and to bench service the down meter. It is also necessary to maintain a substantial inventory of postage meters available for exchange purposes. This requires a substantial investment on the part of the organization in the postage meter rental business and is reflected in the cost to the customer for his rental of postage meter.
The philosophy of the organization in the postage meter rental business was to provide a rugged postage meter which would withstand maltreatment by the customer without breakdown but still be easily and quickly repairable by their service personnel. This philosophy was reflected in the character and structure of the postage meter made for rental purposes.
Prior postage meters were essentially mechanical and relatively limited in scope. Postage values to be printed were entered into the device by the customer and printed by the meter on a label or envelope. The postage values so printed were accounted for by use of an ascending register. The register provided a record of the amount of postage printed over the life of the meter. As postage meters became more advanced, a piece count register was added to the meter to provide information on the number of pieces of mail which were passed through and printed with postage by the meter. An additional feature, which permitted pre-payment by the customer of a desired dollar amount of postage the meter may print, brought about the use of a descending register to indicate the dollar amount of postage left to be dispensed by the meter, before expiration of the pre-paid amount.
The data set forth in the various registers provide the customer with a reasonably full accounting of the postage actively handled by the meter for the customer. The ascending and the descending registers provide a running inventory of the dollar amount of postage already dispensed against the last pre-payment made and the dollar amount of postage available to be dispensed out of the last pre-payment or advanced payment of postage made by the customer, for the meter.
The electronic age brought a change in postage meters in which a central processing unit (CPU), such as a micro-computer or microprocessor, provides calculation and data flow control of postage dispensed and available, in accordance with input data provided. Devices of this nature are taught and described in U.S. Pat. No. 3,978,457. Coupled to the CPU may be a PROM, serving as a permanent memory, for storing program information and other information and a RAM, serving as a temporary memory, for routine storing and working data in real time in coordination with calculations and operations carried on and/or controlled by the CPU. In postage meters, where it is very important to provide permanent and/or non-destructive storage location for accounting data, such as postal funding data, for example, a nonvolatile memory (NVM) is also coupled to the CPU. NVM storage has been used successfully over other known mass data storage devices such as magnetic tape or discs, which are not as secure as NVM storage and are more expensive than NVM storage devices. The use of the NVM storage device in association with a microcomputer is disclosed in U.S. Pat. No. 4,335,434, which describes how to avoid loss of data deposited in a memory device, when the system inadvertently loses power, by use of energy stored in capacitors to provide power to the microcomputer and NVM to enable continued operation for a short period during power loss.
U.S. Pat. No. 4,481,604 describes another arrangement in which battery backed, dual identical CMOS memories, which are essentially NVM devices, are used both for real time accounting registers and for permanent data storage. In the '604 patent, dual, identical battery backed CMOS memories are utilized for storing the same data in corresponding registers thus having a duplication of data in duplicate memory storage systems. The data in the respective registers is periodically compared and any difference in data is used as a non-resettable fatal error in the system, thus causing a down postage meter.
A more advanced system data storage system for use in postage meters is taught and described in co-pending U.S. patent application Ser. No. 718,618, now abandoned, assigned to the same assignee as the present patent application in which a CPU provides data flow for storage in two separate storage units, providing a main set of registers and an alternate set of registers storing corresponding data. The said co-pending application teaches that the two separate data storage units maybe separate memory devices or may be the same memory device partitioned into two separate sections.
It has been found that the transfer of data from a CPU to an NVM is subject to various errors. Various transients that may occur can cause improper reading and/or improper writing of data. It has been known for transients to result in the writing of proper data at the wrong address. While the dual storage of data system adds integrity to data storage and the said co-pending patent application provides an economical solution to the problems in dual data storage system by partitioning an NVM device into two separate sections or using two non-identical NVM devices so as to have a primary set of registers and a secondary set of registers for storing duplicated postage accounting data, it is seen that this technique goes far in solving the problems attendant data recovery but these advances do not lengthen substantially the field life of the postage meter.
The more modern philosophy in the postage meter business is to keep the postage meter in the field with the objective of reducing the service burden placed on rental costs, generating better customer satisfaction and creating better customer relations.
The present invention addresses the problem of field life of the postage meter and provides a novel improved memory system that is effectively self correcting, should a non-correctable error or malfunction occur in the NVM system which would other-wise cause the postage meter to be recalled from the field for service.
It should be kept in mind that while the present invention is described and its use explained with respect to use in a postage meter, the utility of the present novel memory system may be extended to any inventory keeping or accounting system which employs a nonvolatile memory to store data for later recovery for inventory and/or accounting or other purposes.